Active pressure relief valve system and method

ABSTRACT

An active pressure relief valve system and method for lubricating an internal combustion engine includes a reservoir, a pump for pumping fluid from the reservoir through the internal combustion engine, and an active relief valve fluidly disposed downstream from the pump for both variably adjusting pressure of the fluid within the internal combustion engine and limiting the pressure of the fluid within the internal combustion engine to a maximum pressure threshold. The active relief valve is configured to variably and electronically adjust the pressure of the fluid within the internal combustion engine when commanded by a controller, and further configured to mechanically limit the pressure of the fluid within the internal combustion engine to a maximum pressure threshold.

BACKGROUND

Conventional vehicles typically use mechanical oil pumps to provide the necessary oil flow and pressure for internal combustion engine operation and durability. For example, in one arrangement, a single gerotor mechanical pump is permanently driven by the internal combustion engine's crank shaft. Some vehicle manufacturers have begun to introduce advanced mechanical oil pump designs, including variable displacement in an attempt to reduce the power consumption of the pump associated with unnecessarily high engine supply oil pressure. The relief systems associated with conventional oil pumps typically employ a single or double stage mechanical relief system to reduce the pumping losses of the mechanical pump. One known design employs a single electric solenoid valve in addition to a standard mechanical relief valve. This allows control of the single electric solenoid valve by a controller (e.g., providing an additional bypass) to increase engine efficiency through reduction of oil pump pressure pumping losses.

Power consumption in a gerotor-style mechanical oil pump is comprised of two main components: mechanical friction and pumping friction. The mechanical friction of the pump is generally determined by pump component materials, manufacturing precision, and other physical pump-related variables. The mechanical friction of the oil pump can usually only be reduced by changing the physical design of the pump, and results in a constant friction (i.e., power loss) value across varying pump outlet pressures for a given engine/pump speed. The pumping friction of the mechanical pump increases linearly with output pressure for a given engine speed. As the oil pressure necessary for complete operation and durability of the engine is not singularly a function of engine speed, increases in engine efficiency can be realized through adaptive control of engine oil pressure. The use of a mechanical relief valve limits the adaptability of a relief function to control through other mechanical engine characteristics, i.e., pressure, speed, temperature, etc. The operation of a mechanical valve generally cannot adapt to complex real-time changes in engine operation and oil pressure requirements.

Some vehicle manufacturers have begun to add additional electric solenoid relief valves to oil systems to increase the pressure adaption capability of the system. However, known applications typically utilize small, dual position solenoid valves, i.e., toggle-type valves with on or off operation. This limits the capability of the relief valve to areas with large pressure reduction potential and cannot be utilized to actively modify the engine supply pressure under all conditions due to the dual operation solenoid having a single size orifice. When the valve is open, the orifice is an additional flow area that will act to reduce the oil pump outlet pressure. An electric solenoid used in conjunction with a standard mechanical relief valve will increase the adaptability of the pressure supply system and decrease the power consumption of the oil pump; however, without active control over the effective size of the relief system orifice, full adaptability and maximum oil pump efficiency cannot be realized.

Current concerns with the application of a variable orifice size pressure relief primarily concern packaging and cost. Known proportional valves that will produce the required orifice area range require large input torques to operate and induce significant flow restrictions, even when open to the maximum orifice size. Additionally, the added power consumption of the proportional valve could offset the power consumption reduction of the pressure reduction, rendering the system null from a power consumption and efficiency standpoint. Powerful proportional valves that could provide the required flow rate and pressure drop requirements tend to be very large and heavy. From a packaging and fluid flow standpoint, the physical space required also poses significant problems.

SUMMARY

According to one aspect, an active pressure relief valve system for lubricating an internal combustion engine includes a reservoir, a pump for pumping fluid from the reservoir through the internal combustion engine, and an active relief valve fluidly disposed downstream from the pump for both variably adjusting pressure of the fluid within the internal combustion engine and limiting the pressure of the fluid within the internal combustion engine to a maximum pressure threshold. The active relief valve is configured to variably and electronically adjust the pressure of the fluid within the internal combustion engine when commanded by a controller, and further configured to mechanically limit the pressure of the fluid within the internal combustion engine to the maximum pressure threshold.

According to another aspect, an active oil pressure relief valve for a vehicle includes a valve assembly disposed within a relief bore. The relief bore is fluidly connected downstream to a pump for pumping fluid from a reservoir and arranged to selectively return the fluid to the reservoir to variably control the pressure of the fluid and to limit a maximum pressure of the fluid. The active oil pressure relief valve further includes an actuator of the valve assembly rotatably movable to variably control the pressure of the fluid and a piston of the valve assembly axially movable to limit the maximum pressure of the fluid. The piston is axially displaced when the fluid reaches the maximum pressure and thereby passes through the valve assembly back to the reservoir.

According to a further aspect, an active pressure relief valve method for lubricating an internal combustion engine includes providing an active relief valve fluidly disposed downstream from a pump fluidly connected to a fluid reservoir for variably adjusting pressure of a fluid pumped by the pump within the internal combustion engine and limiting the pressure of the fluid within the internal combustion engine to a maximum pressure threshold, variably and electronically adjusting the pressure of the fluid within the internal combustion engine via a controller operatively connected to the active relief valve, and passively and mechanically limiting the pressure of the fluid within the internal combustion engine to a maximum pressure threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an active pressure relief valve system according to an exemplary embodiment.

FIG. 2 is a perspective view of an active pressure relief valve of the active pressure relief valve system of FIG. 1.

FIG. 3 is an exploded perspective view of the active pressure relief valve of FIG. 2.

FIG. 4 is a partial cross-sectional view showing the active pressure relief valve both variably adjusted to a closed position and mechanically held in a closed position.

FIG. 5 is a partial cross-sectional view of the active pressure relief valve similar to FIG. 4 but showing the active pressure relief valve variably adjusted to allow fluid flow therethrough.

FIG. 6 is a partial cross-sectional view of the active pressure relief valve similar to FIG. 4 but showing a piston of the valve mechanically forced open against the urging of a spring.

FIG. 7 is a top view of the active pressure relief valve showing apertures through the piston fully closed by a rotatable member.

FIG. 8 is a view similar to FIG. 7 but showing the rotatable member rotated to partially open the apertures for variably adjusting pressure.

FIG. 9 is another view similar to FIG. 7 but showing the rotatable member fully rotated so that corresponding apertures therethrough are in registry with the apertures through the piston.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for purposes of illustrating one or more exemplary embodiments and not for purposes of limiting same, FIG. 1 schematically illustrates an active pressure relief valve system 10 for lubricating an internal combustion engine 12 on an associated vehicle (not shown). The active pressure relief valve system 10 includes a reservoir 14 of fluid 16, such as oil, and a pump 18 for pumping the fluid 18 from the reservoir 14 through the internal combustion engine 12. The active pressure relief valve system 10 further includes an active relief valve 20 (also referred to herein as an active oil pressure relief valve for a vehicle) fluidly disposed downstream from the pump 18 for both variably adjusting pressure of the fluid 16 within the internal combustion engine 12 and limiting the pressure of the fluid 16 within the internal combustion engine 12 to a maximum pressure threshold. As described in more detail below, the active relief valve 20 is configured to variably and electronically adjust the pressure of the fluid 16 within the internal combustion engine 12 when commanded by a controller 22 and further configured to mechanically limit the pressure of the fluid 16 within the internal combustion engine 12 to the maximum pressure threshold. In the illustrated embodiment of FIG. 1, the controller 22 is an electronic control unit and can be the main electronic control unit provided on the vehicle, though this is not required. Optionally, a filter (not shown) may be fluidly downstream of the pump 18 and upstream from the active relief valve 20.

With additional reference to FIGS. 2 and 3, the active relief valve 20 of the illustrated embodiment includes a valve assembly 30 disposed within a relief bore 32. The relief bore 32 is fluidly connected to and arranged downstream from the pump 18. The relief bore 32 is particularly arranged to allow the active relief valve 20 to selectively return the fluid 16 pumped by the pump 18 to the reservoir 14 to variably control the pressure of the fluid and to limit a maximum pressure of the fluid 16 within the internal combustion engine 12. In the illustrated embodiment, the relief bore 32 is fluidly connected to a main passage 34 defined through the internal combustion engine 12 for diverting a portion of the fluid 16 passing through the main passage 34 and returning the fluid 16 to the reservoir 14 via the active relief valve 20. For this purpose, the active relief valve 20 includes an actuator 36 of the valve assembly 30 that is rotatably movable to variably control the pressure of the fluid 16 and a piston 38 of the valve assembly 30 that is axially movable to limit the maximum pressure of the fluid 16.

As shown, the valve assembly 30 can include a spring 40, in addition to the actuator 36 and the piston 38, for urging the piston 38 toward a closed position (the position of the piston 38 shown in FIGS. 4 and 5). The piston 38 is movable axially against the urging of the spring 40 to an open position (the position of the piston 38 shown in FIG. 6, for example) when the pressure of the fluid 16 reaches or exceeds the maximum pressure. The spring 40 can be selected so that its spring characteristics (e.g., spring coefficient) corresponds to the maximum pressure (i.e., the piston 38 is only movable to compress the spring 40 when the pressure within the internal combustion engine 12 reaches or exceeds the maximum pressure). In one embodiment, the spring 40 is selected so that the maximum pressure is approximately 70 psi, though other maximum pressures could be used as will be known and appreciated by those skilled in the art.

In addition to the actuator 36, the piston 38 and the spring 40, the valve assembly 30 can further include a rotatable member 44 that is rotatable by the actuator 36 for variably adjusting pressure within the internal combustion engine 12. As will be described in more detail below, the actuator 36 variably and electronically adjusts the pressure of the fluid 16 within the internal combustion engine 12 via rotational movement of the rotatable member 44 and the piston 38 is movable against urging of the spring 40 to mechanically limit the pressure of the fluid 16 within the internal combustion engine 12 via axial movement. The piston 38 is axially displaced when the fluid 16 reaches (or exceeds) the maximum pressure and thereby passes through the valve assembly 30 back to the reservoir 14. In an exemplary embodiment, the actuator 36 is a motor that rotatably moves the rotatable member 44 under command by the controller 22 to variably change a cross-sectional opening through the active relief valve 20 to thereby variably adjust fluid pressure within the internal combustion engine 12.

More specifically, the piston 38 can include at least passage therethrough partially defined by at least one axial throughole. In the illustrated embodiment, the at least one axial throughole is a plurality of axial througholes 42 a, 42 b, 42 c defining a plurality of corresponding passages through the piston 38. The rotatable member 44 is variably and rotatably movable between a first rotatable position and a second rotatable position for variably opening or closing the at least one axial throughole (i.e., the axial througholes 42 a, 42 b and 42 c in the illustrated embodiment). As will be described in more detail below, the first position for the rotatable member 44 allows relatively more fluid flow through the at least one axial throughole than the second position. In an exemplary embodiment, a degree of rotation of the rotatable member 44 by the actuator 36 corresponds to a degree of opening of the at least one axial throughole (and therefore also a degree of opening of the at least one passage) by the rotatable member 44.

In particular, the piston 38 of the illustrated embodiment includes a radial wall portion 38 a through which the at least one passage is defined (i.e., the axial througholes 42 a, 42 b, and 42 c are defined in the radial wall portion 38 a) and a cylindrical sleeve wall portion 38 b depending from the radial wall portion 38 a. By this arrangement, the rotatable member 44 can be cooperatively received radially and axially within the cylindrical sleeve wall portion 38 b. The rotatable member also includes at least one corresponding axial throughole, which is a plurality of corresponding througholes 46 a, 46 b and 46 c in the illustrated embodiment. In particular, the corresponding plurality of axial througholes 46 a, 46 b, 46 c correspond with the axial througholes 42 a, 42 b and 42 c of the piston 38. The rotatable member 44 is rotatable by the actuator 36 from the first rotatable position wherein the plurality of axial througholes 42 a, 42 b, and 42 c and the corresponding plurality of axial througholes 46 a, 46 b, 46 c are misaligned (e.g., fully misaligned) to inhibit flow through the at least one passage and a second rotatable position wherein the plurality of axial througholes 42 a, 42 b, 42 c and the corresponding plurality of axial througholes 46 a, 46 b, 46 c are aligned (e.g., in registry with one another). As shown, the rotatable member 44 of the illustrated embodiment has a cup-like configuration similar to the piston 38 (and can alternately be referred to as an inner piston 44). In particular, in the illustrated embodiment, the rotatable member 44 includes a radial wall potion 44 a through which the corresponding plurality of apertures 46 a, 46 b and 46 c are defined and a cylindrical sleeve wall portion 44 b depending from the radial wall portion 44 a.

The rotatable member 44 is connected to the actuator 36 by the spring 40 such that rotation of the spring 40 by the actuator 36 causes rotation of the rotatable member 44 relative to the piston 38. More particularly, in the illustrated embodiment where the actuator 36 is a motor, an output shaft 36 a of the actuator 36 can be connected to the rotatable member 44 by the spring 40 for transferring rotation movement of the output shaft 36 a to the rotatable member 44. In the illustrated embodiment, and with particular reference to FIG. 3, a relief cap 50 is non-rotatably fixed to the actuator 36 by a suitable fastener, such as the illustrated screw 52. As shown, the relief cap 50 includes a head portion 50 a and a threaded shaft portion 50 b extending therefrom. The threaded shaft portion 50 b is appropriately sized for a threaded engagement with a threaded portion 32 a of the relief bore 32 defined in the internal combustion engine 12. This threaded engagement secures the active relief valve 20 within the relief bore 32 of the internal combustion engine 12. Received within the threaded shaft portion 50 b of the relief cap 50 is a thrust bearing 54 that allows relative rotation as will be described below.

The spring 40 includes a first end 40 a received within and non-rotatably fixed to the rotatable member 44. In particular, the first end 40 a of the spring 40 is received within a groove inside the cylindrical sleeve wall portion 44 b of the rotatable member 44. A second end 40 b of the spring 40 is non-rotatably fixed to a spring base 56. In particular, the second end 40 b is received within a circumferential groove 56 a defined on a shaft portion 56 b of the spring base 56. The shaft portion 56 b extends from a head portion 56 c that rests against the thrust bearing 54 and is able to rotatably move relative to the relief cap 50 easily due to the thrust bearing 54. As shown, the relief cap 50, the thrust bearing 54 and the spring base 56 can all be annularly disposed about the output shaft 36 a of the actuator 36. A locknut 58 can be threadedly received on the output shaft 36 a for axially securing the relief cap 50, the thrust bearing 54 and the spring base 56 to the actuator 36. The non-rotatable fixing of the first and second ends 40 a, 40 b of the spring 40, respectively to the rotatable member 40 and the spring base 56 can be through any known connection type, including but not limited to welding, staking, interference fit connection, etc.

To allow the actuator 36 to rotate the spring 40 and thereby the rotatable member 44 relative to the piston 38, one of the piston 38 and a wall 60 of the internal combustion engine 12 defining the relief bore 32 in which the active relief valve 20 is disposed includes a protrusion 62 and the other of the piston 38 and the wall 60 includes an aperture 64 in which the protrusion 62 is received to prevent relative rotation between the wall 60 and the piston 38. In the illustrated embodiment, the protrusion 62 extends radially outward from the cylindrical sleeve wall portion 38 b of the piston 38 and the aperture 64 is defined in the wall 60 of the internal combustion engine 12 (see FIGS. 4-6). It is to be appreciated by those skilled in the art that the protrusion could be provided on the wall 60 and the aperture 64 defined in the piston 38.

Returning reference to FIG. 1, the active pressure relief valve system 10 can include the controller 22 operatively connected to the actuator 36. In particular, the controller 22 can command the active relief valve 20 to variably adjust the pressure of the fluid 16 within the internal combustion engine 12. In addition, the active pressure relief valve system 10 can include a pressure sensor 70 operatively connected to the controller 22 that senses the pressure of the fluid 16 within the internal combustion engine 12 and sends a signal to the controller 22 that is indicative of the pressure sensed. The controller 22 can be configured to variably adjust the pressure of the fluid 16 based on the signal from the pressure sensor 70. In the illustrated embodiment, the pressure sensor 70 is associated with a pressure sensor passage 72 that is fluidly connected to the main passage 34.

The active pressure relief valve system 10 of the illustrated embodiment further includes a first discharge passage 74 fluidly connected to the relief bore 32 for discharging the fluid 16 passing through the relief valve 20 to variably adjust the pressure of the fluid 16 of the internal combustion engine 12 and a second discharge passage 76 fluidly connected to the relief bore 32 for discharging the fluid 16 passing through the relief valve 20 to limit the pressure of the fluid 16 in the internal combustion engine to the maximum pressure threshold.

Though not shown, the actuator 36 can include a torsion spring that urges the output shaft 36 a in a first rotatable direction when the actuator 36 is not commanded by the controller 22. Such rotation is, in turn, transmitted through the spring 40 to thereby urge the rotatable member 44 toward the second rotatable position so that when the controller 22 is not commanding the pressure relief valve 20, the rotatable member 44 moves toward the second rotatable position. In the second rotatable position, the rotatable member can fully close the axial througholes 42 a, 42 b, 42 c as best shown in FIG. 7. When the rotatable member 44 is in the second rotatable position illustrated in FIG. 7 and the pressure of the fluid 16 in the main passage 34 is below the maximum pressure threshold, the active relief valve 20 will be as shown in FIG. 4 and no fluid flow of the fluid 16 will occur through the valve 20 to the first and second discharge passages 74, 76.

Optionally, an indicator 78 can be operatively connected to the controller 22. The indicator 78 can be activated when there is a failure of the active relief valve 20. For example, when the actuator 36 fails to operate as expected when commanded by the controller 22, the controller 22 can activate the indictor 78. The indicator 78 could be, for example, a visual indictor that is illuminated on the dashboard of the vehicle in which the engine 12 is disposed.

In operation, when the controller 22 commands the actuator 36 to rotate, the rotatable member 44 is rotated via the output shaft 36 a and the spring 40 relative to the piston 38. Such rotation causes the corresponding plurality of througholes 46 a, 46 b, 46 c to begin aligning with the axial througholes 42 a, 42 b, 42 c as shown in FIG. 8 and thereby allow the fluid 16 to pass through the piston 44, and more generally through the active relief valve 20 and onto the first discharge passage 74 as shown in FIG. 5. The degree of rotation of the rotatable member 44 corresponds to a degree of alignment between the corresponding plurality of apertures 46 a, 46 b, 46 c and the axial througholes 42 a, 42 b, 42 c of the piston 38. The first rotatable position for the rotatable member 44 can correspond to the corresponding plurality of apertures 46 a, 46 b, 46 c being in registry with the axial througholes 42 a, 42 b, 42 c, and thus a maximum opening amount is provided through the piston 38 when the rotatable member 44 is rotated to the first rotatable position as illustrated in FIG. 9. As already mentioned, the degree to which the rotatable member 44 is rotated and thus the degree to which the axial througholes 42 a, 42 b, 42 c in the piston 38 are opened can be controlled by the controller 22 based on the sensed pressure within the main passage 34.

In the illustrated embodiment, the first position for the rotatable member 44 is a position wherein the corresponding axial througholes 46 a, 46 b, 46 c are fully in registry with the axial througholes 42 a, 42 b, 42 c and the second position is a position wherein the corresponding axial througholes 46 a, 46 b, 46 c are fully misaligned with the axial througholes 42 a, 42 b, 42 c. This is not required. The first position need only be a position wherein the corresponding axial througholes 46 a, 46 b, 46 c are at least partially in registry with the axial througholes 42 a, 42 b, 42 c and the second position need only be a position wherein the axial througholes are less open than the first position.

Under normal operating conditions, the system 10 can operate in a computer controlled feedback loop wherein the controller 22 will command a specific required oil pressure based on engine and vehicle operating conditions and the active relief valve 20 will vary the relief flow area to achieve the pressure demanded by the controller 22. If a failure occurs, the system can behave as a standard two-stage mechanical oil pressure relief system. More particularly, in the event of a failure, such as a power failure within the associated vehicle whereby command of the actuator 36 by the controller 22 ceases, the torsion spring within the actuator 36 operates to return the output shaft 36 a and the rotatable member 44 to the second position wherein the rotatable member 44 inhibits flow through the axial througholes 42 a, 42 b, 42 c (FIG. 7). Should pressure of the fluid 16 within the main passage 34 exceed the maximum pressure threshold, the fluid 16 will axially move the piston 38 as shown in FIG. 6 against the urging of the spring 40 and allow fluid flow from the main passage 34 through the second discharge passage 76. Accordingly, the active relief valve 20 mechanically limits the pressure of the fluid 16 within the internal combustion engine 12 to the maximum pressure threshold because excess pressure within the main passage 34 causes the active relief valve 20 to open fluid flow from the main passage 34 through the second discharge passage 76. In addition, the rotatable member can be rotatably moved by the actuator 36 based on commands from the controller 22 so that, under normal operating conditions, the pressure of the fluid 16 within the internal combustion engine 12 can be variably and electronically adjusted.

Advantageously, the active relief valve 20 being configured to variably and electrically adjust the pressure of the fluid 16 within the internal combustion engine 12 and further configured to mechanically limit the pressure of the fluid 16 within the internal combustion engine 12 to the maximum pressure threshold occurs within a single active relief valve 20 that is disposed within only a single relief bore 32 defined within the internal combustion engine 12. Functionally, the system 10 behaves as an independently controlled dual-stage relief system with one mechanical non-active relief and one electro-mechanical active relief operating in conjunction to control the engine oil pressure to a target value. Structurally, the active relief valve 20 is located in the same space envelope as a conventional standard mechanical system. Advantageously, this reduces the number of modifications that would be needed to adapt the system to a current conventional engine or oil pump structure. In addition, the active pressure relief valve system allows for complete active control of the engine operating oil pressure while ensuring the durability and reliability of the engine 12 during any failure condition. The control of the oil pressure will allow the engine 12 to operate more efficiently but will also continue to protect the engine from excessive pressures.

An active pressure relief valve method for lubricating an internal combustion engine will now be described. In particular, the method will be described in association with the active pressure relief valve system 10 described hereinabove, though this is not required. In the method, the active relief valve 10 that is disposed downstream from the pump 18 and fluidly connected to the fluid reservoir 14 is provided for both variably adjusting pressure of the fluid 16 pumped by the pump 18 within the internal combustion engine 12 and limiting the pressure of the fluid 16 within the internal combustion engine 12 to the maximum pressure threshold. The pressure of the fluid 16 within the internal combustion engine 12 is variably and electronically adjusted via the controller 22 operatively connected to the active relief valve 20. The pressure of the fluid 16 within the internal combustion engine 12 is also passively and mechanically limited to a maximum pressure threshold. As already described herein, adjusting the pressure of the fluid 16 variably and electronically can include controlling the actuator 36 to rotatably move the active relief valve 20, and limiting the pressure of the fluid 16 can passively and mechanically can include urging the piston 38 via the spring 40 toward the closed position (shown in FIG. 5) for inhibiting passage of the fluid 16 until the pressure reaches the maximum pressure threshold.

It will be appreciated that various of the above-disclosed and other features and functions, or alternatives or varieties thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. 

1. An active pressure relief valve system for lubricating an internal combustion engine, comprising: a reservoir; a pump for pumping fluid from the reservoir through the internal combustion engine; and an active relief valve fluidly disposed downstream from the pump for both variably adjusting pressure of the fluid within the internal combustion engine and limiting the pressure of the fluid within the internal combustion engine to a maximum pressure threshold, the active relief valve configured to variably and electronically adjust the pressure of the fluid within the internal combustion engine when commanded by a controller and further configured to mechanically limit the pressure of the fluid within the internal combustion engine to the maximum pressure threshold.
 2. The active pressure relief valve system of claim 1 wherein the active relief valve includes: an actuator that variably and electronically adjusts the pressure of the fluid within the internal combustion engine via rotational movement; and a piston movable against urging of a spring that mechanically limits the pressure of the fluid within the internal combustion engine via axial movement.
 3. The active pressure relief valve system of claim 2 wherein the active relief valve is disposed within only a single relief bore defined within the internal combustion engine.
 4. The active pressure relief valve system of claim 2 wherein the piston includes at least one axial throughole and the active relief valve includes a rotatable member variably and rotatably movable between a first position and a second position for variably opening or closing the at least one axial throughole, the first position allowing relatively more fluid flow through the at least one axial throughole than the second position.
 5. The active pressure relief valve system of claim 4 wherein the actuator is a motor that rotatably moves the rotatable member under command by the controller.
 6. The active pressure relief valve system of claim 5 wherein the rotatable member is connected to the motor by the spring such that rotation of the spring by the motor causes rotation of the rotatable member relative to the piston.
 7. The active pressure relief valve system of claim 6 wherein one of the piston and a wall of the internal combustion engine defining a relief bore in which the active relief valve is disposed includes a protrusion and the other of the piston and the wall includes an aperture in which the protrusion is received to prevent relative rotation between the wall and the piston.
 8. The active pressure relief valve system of claim 4 wherein the motor includes a torsion spring that urges the rotatable member toward the second position such that, when the controller is not commanding the pressure relief valve, the rotatable member moves toward the second position.
 9. The active pressure relief valve system of claim 1 further including: the controller that commands the active relief valve to variably adjust the pressure of the fluid within the internal combustion engine; and a pressure sensor operatively connected to the controller that senses the pressure of the fluid and sends a signal to the controller that is indicative of the pressure sensed, and wherein the controller variably adjusts the pressure of the fluid based on the signal from the pressure sensor.
 10. The active pressure relief valve system of claim 1 further including: a relief bore defined in the internal combustion engine in which the active relief valve is received; a first discharge passage fluidly connected to the relief bore for discharging the fluid passing through the relief valve to variably adjust the pressure of the fluid of the internal combustion engine; and a second discharge passage fluidly connected to the relief bore for discharging the fluid passing through the relief valve to limit the pressure of the fluid in the internal combustion engine to the maximum pressure threshold.
 11. The active pressure relief valve system of claim 1 wherein an indicator is operatively connected to the controller, the indicator activated when there is a failure of the active relief valve.
 12. An active oil pressure relief valve for a vehicle, comprising: a valve assembly disposed within a relief bore, the relief bore fluidly connected downstream to a pump for pumping fluid from a reservoir and arranged to selectively return the fluid to the reservoir to variably control a pressure of the fluid and to limit a maximum pressure of the fluid; an actuator of the valve assembly rotatably movable to variably control the pressure of the fluid; and a piston of the valve assembly axially movable to limit the maximum pressure of the fluid, the piston axially displaced when the fluid reaches the maximum pressure and thereby passing through the valve assembly back to the reservoir.
 13. The active pressure relief valve of claim 12 wherein the valve assembly includes a spring for urging the piston toward a closed position, the piston movable axially against the urging of the spring when the pressure of the fluid reaches the maximum pressure.
 14. The active pressure relief valve of claim 13 wherein the valve assembly includes a rotatable member that is rotatable by the actuator for selectively opening and closing at least one passage defined through the piston, and wherein a degree of rotation of the rotatable member by the actuator corresponds to a degree of closure of the at least one passage by the rotatable member.
 15. The active pressure relief valve of claim 14 wherein the piston includes a radial wall portion through which the at least one passage is defined and a cylindrical sleeve wall portion depending from the radial wall portion, and wherein the rotatable member is cooperatively received radially and axially within the cylindrical sleeve wall portion.
 16. The active pressure relief valve of claim 14 wherein the at least one passage is a plurality of axial througholes defined through the piston and the rotatable member includes a corresponding plurality of axial througholes defined therethrough, the rotatable member rotatable by the actuator from a first rotatable position wherein the plurality of axial througholes and the corresponding plurality of axial througholes are misaligned to inhibit flow through the at least one passage and a second rotatable position wherein the plurality of axial througholes and the corresponding plurality of axial througholes are in registry with one another.
 17. The active pressure relief valve of claim 13 wherein the actuator is a motor having an output shaft connected to the rotatable member by the spring for transferring rotation movement of the output shaft to the rotatable member.
 18. The active pressure relief valve of claim 12 further including a controller operatively connected to the actuator for control thereof based on a sensed pressure of the fluid.
 19. An active pressure relief valve method for lubricating an internal combustion engine, comprising: providing an active relief valve fluidly disposed downstream from a pump fluidly connected to a fluid reservoir for both variably adjusting pressure of a fluid pumped by the pump within the internal combustion engine and limiting the pressure of the fluid within the internal combustion engine to a maximum pressure threshold; variably and electronically adjusting the pressure of the fluid within the internal combustion engine via a controller operatively connected to the active relief valve; and passively and mechanically limiting the pressure of the fluid within the internal combustion engine to a maximum pressure threshold.
 20. The method of claim 19 wherein variably and electronically adjusting the pressure of the fluid includes controlling an actuator to rotatably move the active relief valve, and passively and mechanically limiting the pressure of the fluid includes urging a piston via a spring toward a closed position for inhibiting passage of the fluid until the pressure reaches the maximum pressure threshold. 